The screw cap is one of the mainly used closing systems for bottles and for containers for liquids in general, particularly for products of wide consumption, both for economic reasons owing to its moderate cost thereof, and also for its technical features suitable for guaranteeing the optimal sealing of the liquid inside the bottle and also appreciated flexibility in terms of visual impact.
This kind of cap has also the advantage of a very easy manual opening, that does not require the use of special devices such as corkscrews, as well as easy reclosing for leakage-proof conservation of the liquid in case remained into the bottle.
The screw cap may be made wholly of plastic material, or metallic material, with a metallic capsule and an internal seal of plastic material.
The screw cap is generally constituted of a capsule, that is a cup shaped body, having a thread, or one or more thread portions, at the inner part of the substantially cylindrical tract thereof.
Along the edge of the capsule it is generally provided a security ring, of the strip kind, that is fixed to the edge by means of a plurality of bridge elements to be broken upon the first unscrewing of the cap from the neck of the bottle to which the cap is screwed.
Such a security ring is made integral with the internally threaded capsule. Such a ring, consistently with the technical bounds of the mould, is shaped so as to surround the neck of the bottle below the thread and an adjoining anti-extraction shoulder, suitable for avoiding the raising of the security ring.
The security ring is so shaped to be blocked under said anti-extraction shoulder at the first unscrewing, so that the user, by continuing with the unscrewing, causes the breakage of the bridge elements and the detachment of the security ring, the latter remaining to surround the neck of the bottle to show the opening of the bottle.
Such screw caps, despite being appreciated and used, have some disadvantages.
The plastic caps, usually made monolithically with the safety ring, due to limits of the moulds, have a security ring that, due to the necessity of extracting by pulling out the moulded cap from the mould, does not extend radially towards the inner above a certain limited length fixed by the necessity of extracting the piece from the mould without breaking it.
The limit for the development of the safety ring in the radial direction can cause at the unscrewing of the cap from the bottle, or any other container for liquids to which the cap is associated, the safety ring rather than blocking against the anti-extraction shoulder slide over the anti-extraction shoulder, without tearing from the capsule of the cap, thus failing the function as security element and as opening signal.
The metallic safety rings that are counter-shaped on the same metallic capsule that is in turn semifinished on the neck of the bottle by rolling are safer regarding this aspect guaranteeing the tearing of the ring form the capsule.
On the other hand such metallic screw caps even though being extensively decoratable, have the tearing line that is visible, this being not so much visually pleasant.
Furthermore if the safety ring does not perfectly detach, due to the malleability of the metallic sheet with which the cap is made, it is necessary to intervene by hand or by a tool to complete the detachment.
Furthermore the safety ring fallen to surround the neck of the bottle is usually considered as an aesthetically depriving element, and it is common to remove the safety ring to avoid the movement thereof during the pouring operations to be seen.
A further example of known cap is described in WO00/37329. The cap described in that document consists of two capsules is susceptible of reciprocal separation at the first opening. The opening indication (tamper) is made evident by means of a coloured strip that is made visible as a consequence of the separation of the two capsules. In such a cap the irreversibility of the indication is made by the fact that between the capsules are provided fins that deform by pressing when an attempt is made to reclose the cap on the container.
Since specific means for effectively blocking the capsule one on the other are not provided, the external capsule have an undesired gap both rotational and axial in relation to the internal capsule, the gap jeopardizing the anti-tamper efficacy and the functionality of such a cap.